Proportional solenoid valve

ABSTRACT

A diaphragm operated valve assembly is controlled by an electromagnetic valve assembly. A flat disc armature, which forms part of a flux path, is operable in an inner chamber to modulate the flow between the inner chamber and an exit port in response to an applied magnetic force. The level of the effective magnetic force is a function of the armature mass, and the pressure acting on the disc surface. A pole piece adjacent to the flat disc armature is slidably adjustable to establish a specified force to actuate the armature to the closed or sealing position. This specified force is proportional to the current flow through the winding of the electromagnetic valve assembly. Thus the armature operates to seal communication between the inner chamber and the exit port at a given pressure differential as a function of current flow. The travel distance between the armature and a nonmagnetic seal seat has been minimized by spring biasing the armature in proximity to the seal seat.

This application is a continuation of application Ser. No. 349,488 filedFeb. 17, 1982, now abandoned, which was a continuation-in-part ofapplication Ser. No. 311,820 filed Oct. 16, 1981, now abandoned.

BACKGROUND OF THE INVENTION

The present invention is useful with an electromagnetic solenoid valveoperable for fluid contol in conjunction with a diaphragm operablevalve. Such solenoid valves are known and used to control eitherhydraulic or pneumatic flow. Such valve combinations are often complexassemblies that are spring biased, operable in conjunction withconnecting rods or ball valves, or have flexible diaphragms fabricatedof special material. These devices are responsive to variations incurrent and/or voltage through the solenoid to permit flow through thevalve as a function of fluid flow or pressure. Some of these valvesoperate in a steady state condition (i.e., a direct current flow at agiven voltage) where the forces, such as mechanical spring bias,electromagnetic field, and/or fluid pressure, are balanced or calibratedto permit valve operation in a given mode. These valves are notgenerally electrically adjustable. However, in at least one case thereis an adjustable means, such as a screw, to vary the fluid flow andpressure operable against a bias spring to thereby effect a change inthe operation of the valve. The bias springs of these various devicesare changeable, as are the number of turns of the solenoid coil, thematerials of construction, and the sizes of the assemblies. Thesedevices are somewhat complex and relatively expensive to assemble.

Such solenoid valves find particular application in modern automobilesequipped with various microprocessors that receive input signalsindicating physical parameters such as exhaust gas oxygen content,vehicle speed, engine RPM, engine temperature, and so forth. Suchmicroprocessors receive these input data signals, and evaluate and/orcompare the data to produce a signal which may control fuel input, sparkadvance or other operating parameters. In the present case such amicroprocessor is capable of producing an output signal that willactuate the solenoid valve at a given current amplitude to provide apredictable or desired output from a variable fluid source, such as amanifold vacuum. The microprocessor in the automobile case above cancontrol the duty cycle or on-time of a square wave signal to maintainthe fluid pressure or vacuum output at a desired level for a givenamperage signal. This control can be achieved even though the enginecompartment and solenoid temperatures vary. The current level signal canalso be derived from simpler arrangements, such as a signal generator ora simple power supply, when closed loop control is not required.

Thus the present invention is directed to a less complex valve assembly,and in particular to an assembly which is electromagnetically adjustableand operable in response to a varing input electrical signal.

SUMMARY OF THE INVENTION

The present invention is useful in an electromagnetic solenoid valveassembly having a central bore terminating in a non-magnetic seat withinan interior central chamber having an exit port. There is a flat discarmature or closure member operable in this chamber to contact thenon-magnetic seat and thus seal flow between the bore and the exit port.This device is operable to maintain a specific pressure differentialbetween the central bore and the exit port. The magnetically inducedforce required to operate the magnetic closure member is affected by themass of the magnetic closure member and diameter of the non-magneticseat. The magnetic closure member is perforated, serrated or otherwisemarked to allow fluid flow therethrough for communication between thecentral bore and the exit port. This invention is operable inconjunction with known valve means. Further, the solenoid can be adaptedto be operable either where the fluid pressure is used to control avacuum operable or pressure operable device.

BRIEF DESCRIPTION OF THE DRAWINGS

In the figures of the drawing, like reference numerals identify likecomponents, and in the drawing:

FIG. 1 is a side view of the valve assembly of this invention showingthe power supply connection;

FIG. 2 is a vertical sectional view of the proportional solenoid valveof this invention, taken on a scale enlarged with respect to the scaleof FIG. 1;

FIG. 3 is a plan view of a closure member shown in FIG. 1;

FIG. 4 is a sectional view of an alternative embodiment of theproportional solenoid valve;

FIG. 5(A) is a plan view of the mounting bracket;

FIG. 5(B) is a side view of the mounting bracket;

FIG. 6 is an enlarged view of the non-magnetic seat and magnetic controlmember assembly;

FIG. 7 is a graphical illustration of force versus stroke (traveldistance of an armature) for a solenoid type device;

FIG. 8 is a graphical illustration of the linear output of theinvention;

FIG. 9 graphically illustrates a plot of empirical data for a pressuredifferential as a function of current;

FIG. 10 graphically illustrates temperature effects on the operation ofthis invention;

FIG. 11 is an enlarged view of an alternative embodiment of a one-piecesleeve and nonmagnetic seat assembly;

FIG. 12 is an enlarged view of an alternative embodiment of anonmagnetic seat and bobbin one-piece assembly; and

FIG. 13 is a vertical sectional view of alternative embodiment of theproportional solenoid valve.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

An electromagnetic valve assembly 10 constructed in accordance with theinvention is shown in FIG. 1 as vertically oriented, and is illustratedas cooperating with a diaphragm operated valve assembly 12 to form anoperating combination 11 for use in a vehicle or other apparatus. Theoperating combination 11 is coupled between a vacuum source 300 and avacuum operable motor 301. A vacuum, in the sense used herein, is apressure below atmospheric pressure. The electromagnetic valve assembly10 includes an outer member or a mounting bracket 14 in FIGS. 2, 5A and5B, having a top 13 and a bottom 15, a hollow cylindrical magnetic corepole piece or center member 16, an electrical winding 18 mounted aboutcenter member 16, a non-magnetic material seat 20 with a lower face 21(see FIG. 6), an annular magnetic closure member 22 (FIG. 3), and a basemember 23 which defines at least one aperture 129. Shown in FIG. 1 areelectrical connecting means 150, in this case a pair of terminals,connectible over a pair of conductors 154 to a suitable power supply152. The power supply can be a direct current source, a square wavegenerator, a variable resistor, a pulse width modulation circuit, or anautomobile on-board computer functioning as a signal source.

Pole piece 16 defines a cylindrical central passage or bore 24 with aninlet port 26 and an exit port 28. Mounted about pole piece 16 is acylindrical sleeve or reference member 30 which is preferably of amagnetic material for improved flux density. The electrical winding 18is encased on its upper, lower and inner diameter surfaces in a bobbin32 generally of plastic material, which bobbin 32 surrounds and engagesthe sleeve 30 and thereby the magnetic pole piece 16 along most of theiraxial dimensions. A subassembly consisting of the pole piece 16, sleeve30, bobbin 32 and electrical winding 18 is mounted on and rigidlymaintained in position in an open faced slot 35 defined by bracket 14(FIG. 5A) and a flange 36 defined by bobbin 32. In this preferredembodiment, an encapsulant 38 surrounds the outer diameter of thewinding 18, although this encapsulant is not a functional requisite. Awasher retainer or top member 40, preferably of a magnetic material, ismounted atop the encapsulant 38 in FIG. 2 and defines an aperture 42.The pole piece 16 and sleeve 30 protrude through aperture 42. Bracket 14defines tabs 43 at its upper extremity which are formed overwasher-retainer 40 to secure said retainer 40 and the subassembly inbracket 14.

As shown in FIG. 6, pole piece 16 defines a seal slot 46 near itslowermost portion, and pole piece 16 terminates in a flange or rightangular foot 44 having an outer diameter 47 and a lower surface 45.Sleeve 30 at its lower extremity defines a flange 48 with outer diamter49, and a counterbore 50 with a wall 51. Non-magnetic seat 20 definesshoulder 52, an aperture 53, wall 54 having outer surface 56 and aninner surface 58, and a diameter noted as `y` in FIG. 6. Outer diameters47 and 49 of flanges 44 and 48, respectively, are equal and contactinner surface 58 of seat 20. Flange 48 of sleeve or reference member 30abuts shoulder 52 and is press fit and retained in aperture 53. Polepiece 16 is adjustable along its vertical axis to abut flange 48 withflange 44 or to bring lower surface 45 of pole piece or center member 16into closer proximity with the lower face 21 of seat 20 and closuremember 22. Thus, pole piece 16 is adjustable to meet a specified forcerequirement that is a function of distance.

Alternative embodiments of the pole piece 16, seat 20 and sleeve 30configuration are illustated in FIGS. 11 and 12. FIG. 11 depicts anassembly where sleeve 30 and nonmagnetic seat 20 are shown as a single,drawn, nonmagnetic element 231 which are of a thin-wall tubing material.This tubing thickness can be on the order of 0.012 inch, providing anincreased wall thickness of pole piece 16 to improve magnetic fluxdensity. Nonmagnetic element 231 includes a seat area 233 and a tubularextension 235 having a cylindrical shape. The outer and inner diameterof seat 233 are greater than those dimensions of tubular extension 235,and seat 233 defines a shoulder 237 against which right angle foot 44 ofpole piece 16 may be restrained in its upward travel. Seat 233 furtherdefines lower face 21 for contact with closure member 22. Pole piece 16is again adjustable to meet a specified force requirement as a functionof the distance to closure member 22.

FIG. 12 shows a second alternative embodiment of the nonmagnetic seat 20wherein the seat 20 and bobbin 32 are cast, molded or otherwise formedof a nonmagnetic material as an unitary assembly 240. Assembly 240 inFIG. 12 defines a cylindrical passage 242 to receive a sleeve 244 with awall 246 similar to sleeve 30 of FIGS. 2 and 6 but not having a flange48 which extends beyond the thickness of wall 246. Pole piece 16 isslidable in sleeve 244 and is restrained in its upward travel to contactwall 246 with flange 44. Pole piece 16 is slidable to vary therelationship between flange 44 and seat face 21, and is thus adjustableto meet a specified force requirement as a function of its distance fromclosure member 22. In this embodiment sleeve 244 may be of a magneticmaterial and it may be either thin or thick wall, as it is no longerintegral with the nonmagnetic seat 20 and can be utilized to increasethe magnetic flux density.

In FIG. 2 bobbin 32 defines a shoulder 59. In FIG. 6 outer wall 56 andshoulder 52 of seat 20 bear against and are rigidly retained by shoulder59. The distance between the seat face 21 and the pole piece lowersurface 45, as shown in FIG. 6, is designated as a distance `x`. Agasket 55 for sealing its positioned in seal slot 46 of pole piece 16 tocontact the counterbore wall 51 and provide a seal therebetween. Theattainment of the proper height setting, that is, the distance `x`, isthereafter set by securing pole piece 16 to sleeve reference member 30at its upper surface 60 by any means known in the art, such as welding.A filter 62 is positioned atop pole piece 16 to prevent particulateentrainment through the solenoid valve assembly. Filter 62 can be of acellulose material.

Diaphragm valve operator 12 illustrates the use of the electromagneticvalve assembly 10 to control vacuum supply 300 to a vacuum motor 301.Valve operator 12 has a bottom cover 102 secured to base member 23 by ashell 104. Bottom cover 102 defines a port 106 and passage 108 whichcommunicate to a vacuum source 300. Base member 23 defines neck 110 andflange 112 with a seal slot 114 to receive a gasket or seal 116. Flanges36 and 112 abut each other and seal 116 forms an airtight sealtherebetween. Neck 110 is positioned in slot 35 of bracket 14 to retaindiaphragm valve operator 12 in communication with electromagnetic valveassembly 10. Flange 112 of base member 23 and bobbin 32 cooperate todefine an annular chamber 118 wherein annular magnetic closure member 22is operative to engage seat 20. Closure member 22, shown in FIG. 3, hasan inner face 120 and an overall diameter `z`. Closure member 22 definesapertures 122 which allow fluid communication through member 22. Asshown in FIG. 2, closure member 22 is maintained in close proximity (adistance the order of 0.0015 inch) to nonmagnetic seat 20 with face 21.Generally, seat 20 is of a soft material such as brass and closuremember 22 is of a harder material such as iron or steel such that thisproduces the combination of a soft material touching a harder materialupon contact of these two members. The hard-soft contact provides aminimal deformation but such deformation allows for better seating andtighter sealing as inner face 120 of closure member 22 operates tocontact seat face 21 of seat 20 to thereby restrict communicationbetween passage 24 and chamber 118. Seat 20 can also be a hard materialsuch as nonmagnetic stainless steel or plastic. During normal operation,closure member 22 is maintained in close proximity to seat 20 by aspring 124 mounted on base member 23. Base 23 includes an upstandingcylindrical portion 128 terminating in a generally flat surface area127. Spring 124 is positioned around cylindrical portion 128, andsurface area 127 aids in positioning magnetic closure member 22.Cylindrical portion 128 extends into chamber 118, and its flat surface127 limits the downward travel of closure member 22. The volume ofcylindrical portion 128 also serves to limit the volume of chamber 118,and pressure and volume changes of fluid in chamber 115 are thus morerapid.

The illustrated valve 12 is a dual diaphragm operator with diaphragms200 and 202 in a parallel relationship to each other to definetherebetween an atmospheric chamber 204 which communicates to atmospherethrough a plug 206 defining an aperture 208, which plug 206 is insertedin an opening 210 defined by cover 102. Aperture 208 communicates toatmosphere through port 211 defined by shell 104. Positioned abovepassage 108 is a connecting sleeve 214 having open ports 215 and 217.The valve 12 includes a sealing means 212 which is shown in thereference position of FIG. 2 seated upon connecting sleeve 214 to sealport 215. Movable plates 218, 219 are affixed to the diaphragm operators200 and 202, respectively. The plate 219 defines an annular opening 220,an annular contacting ridge 222, an annular chamber 224 with a capmember 225 inserted therein to seal chamber 224. A spring 216 is seatedagainst a cap member 225 to bias sealing means 212 to contact sleeve 214in the reference position. Sealing means 212 contacts and sealscommunication from sleeve 214 and vacuum source 300 to a chamber 226defined between plate 219 and cover 102. The chamber 226 communicateswith a vacuum motor 301 through a port 228 defined by cover 102 and aconnecting means 230.

Cover 102 defines passages 130 and 132 and orifice 134. Base member 23and plate 218 cooperate to define vacuum chamber 136 therebetween. Avacuum condition is communicable to chamber 136 from the vacuum source300 through passages 130, 132 and orifice 134, and this vacuum iscommunicated to chamber 118 from chamber 136 through aperture 129.

FIG. 13 illustrates an alternative embodiment of the assembly 10 shownin FIG. 2. Bobbin 32 of assembly 10 defines a lower surface 404 open tochamber 118 wherein a bias spring 402 is positioned to abut surface 404and contact annular magnetic closure member 22. Bias spring 402 providesa force acting to maintain said closure member 22 in a normally openrelationship to lower face 21 of nonmagnetic material seat 20. Further,bias spring 20 maintains closure member 22 in its reference positionperpendicular to the vertical axis of bore 24 as shown in FIGS. 2 and13. This action of maintaining the closure member 22 in the referenceposition has been found to prevent "cocking" or angular displacement ofclosure member 22 from the perpendicular relationship to the verticalaxis.

OPERATION

In operation, the closure member 22, shown in FIG. 2 in the referenceposition contacting seat 20, is rapidly responsive to an inducedmagnetic flux from a current at a given voltage passed through theelectrical windings or means for establishing electromagnetic flux 18 ofvalve assembly 10. A magnetic flux path is produced through bracket 14,closure member 22, pole piece 16, sleeve 30, washer retainer 40 and thegap distance between the exit port end of pole piece 16 and closuremember 22. In a steady state condition, that is, when a direct currentis passed through the windings, closure member 22 is drawn toward seat20 and retained in that position until the magnetic flux is interrupted.At current interruption, that is, magnetic flux interruption, theclosure member 22 would fall by gravity and pressure differential to thereference position to rest on spring 124 as shown in FIG. 2 which springis a means to bias closure member 22 to the reference position.

When a pressure depression from atmosphere (i.e., a vacuum) is imposedat port 106, the vacuum condition is communicated to chambers 136 and118 through passages 108, 130 132 and orifice 134. When the vacuum inchamber 136 is great enough to flex diaphragms 200, 202 againstatmospheric pressure, the valve plates 218, 219 move vertically upwardfrom the reference position shown in FIG. 1. As the ridge 222 movesupwardly, it lifts sealing means 212 and provides vacuum communicationbetween passage 108 and chamber 226 through opening 220 and port 215.

In the combination of valves 10 and 12 shown in FIG. 2, a vacuum sourcecommunicates with chamber 118 of electromagnetic valve assembly 10through port 106, passages 108, 130 and 132, orifice 134, chamber 136and aperture 129. Pole piece 16 communicates atmosphere (air) asillustrated through port 26, passage 24 and port 28 to chamber 118.

When electrical winding 18 is energized from power supply 152, amagnetic flux is induced which attracts closure member 22 toward polepiece 16. Seat 20 contacts closure member 22 on inner surface 120, thussealing communication between chamber 118 and passage 24. The force(magnetic flux) required to move closure member 22 is dependent upon themass of closure member 22, the pressure differential between chamber 118and passage 24, and the diameter `y` of seat 20. Diameter `y` of seat 20and the mass of closure member 22 are fixed at the point of assembly.Thus the operational variables affecting movement of closure member 22are the pressure differential and the magnetic force, which isproportional to the current at a voltage through windings 18.

It is known that the force of the magnetic field of an electromagneticvalve is proportional to the power input to the electrical winding asshown in FIG. 7 (Herbert C. Roters, "Electromagnetic Devices", FirstEdition-Tenth Printing 1967 (New York: John Wiley & Sons, Inc., 1941),p. 232). In the present example, where passage 24 is at atmosphericpressure and a vacuum (pressure below atmospheric) is being introducedinto chamber 118, there is a pressure differential operating on innersurface 120 to maintain closure member 22 open. The attractive force ofthe magnetic flux must overcome the mass (about 1.4 grams) of member 22,gravity and the downward pressure force acting on surface 120 tomaintain the closure member 22 seated on spring 124 in the referenceposition. As the mass of member 22 is fixed, the magnetic force requiredto move it is a function of pressure differential. This magnetic forcehas been found to be proportional to the current (amperage) through theelectrical windings 18, as is illustrated in FIG. 8 in the ideal case.An empirical illustration of the change of the pressure differential(vacuum in inches of mercury) as a function of the current inmilliamperes for the invention is given in FIG. 9. The linear functionin FIG. 9 has the appearance of a hysteresis loop, but a straight linefunction is superimposed between those loops as a close approximation ofthe ideal case in FIG. 8. This function of FIG. 9 is for a solenoidhaving 43 ohms resistance, with an electrical input at 160 hertz andoperating against an input vacuum of 14 inches of mercury. Similarcurves have been determined for varying resistances, frequencies andpressure differentials.

It has been found that for a square wave input signal at lowerfrequencies, such as about 80 hertz, there may be a shift in the setpoint for a significant change in the input vacuum level, such as fromfive (5) inches of mercury vacuum to twenty (20) inches of mercuryvacuum. For such low frequency operation, it has been found that orifice134 can be provided with a laminar or jet-flow structure to improvefluid flow characteristics to relieve this set-point shift problem.

Any given point along the straight line function may be selected anddefined as the set point. At this set point, the corresponding amperagefor a solenoid with the characteristics that produced this curve willinduce a magnetic field strong enough to attract closure member 22 toseat 20 against the pressure depression from atmospheric (vacuum) toseal communication between passage 24 and chamber 118.

Thus the operation to contact seat 20 is dependent upon a fixed or givenamperage and will operate to close communication between chamber 118 andpassage 24 when the pressure differential between these volumes is at orbelow the set point along the curve.

It is to be noted that the vacuum condition in chamber 118 iscommunicated through the orifice 134. There is a significant differencebetween the diameters of passage 24 and orifice 134 and seat 20. As anexample, in a given application, the orifice 134 size was about 0.020inch diameter the passage 24 size was about 0.060 inch diameter and seat20 diameter was about 0.300 diameter. However, the pressure differentialbetween chamber 118 and passage 24 is a function of the magnetic forceexerted on the closure member 22, as the distance between seat face 21and closure 22 is very small. The fact that the orifice 134 is shown inthe valve 12 does not affect the operation of the solenoid 10 as asimilar connecting orifice could be positioned in communicating means129 or be integral to valve 10.

The operation of this device is shown as being proportional to a givenelectrical power, amperage or voltage input to the electrical winding18. The curves of the Roters' reference above are shown in FIG. 7 as afamily of curves on Cartesian coordinate axes. As noted, the horizontalaxis is the armature (closure member 22 in our case) stroke length ininches and the vertical axis is force in pounds. In the present case,the armature stroke is a very small incremental distance, that is, onthe order of about 0.0015 inch. However, as there is a fixed distance`x` from pole piece 16 to the lower surface 21 of seat 20, the strokelength distance through which this force must act is (x+0.0015 in.).Therefore, the actual travel of closure member 22 has been minimized formore rapid response and better control. If a vertical pair of lines isdrawn at distances x and x+0.0015 along the horizontal axis in FIG. 7,they would intersect the family of curves at the various amperagelevels. Thus this solenoid operates over a very narrow range of thesevariables, thereby giving better control of its operation to modulatethe flow between the chamber 118 and bore 24.

The solenoid valve will open and close at any set point, that is, anypoint along the straight line function of FIG. 8. In this case, thepressure differential can be selected to respond to a given currentinput or the current input (illustrated on the horizontal axis in FIG.8) can be selected to move closure member 22 at a given pressuredifferential. In either situation, the valve 10 has been found to betemperature insensitive at a given peak amperage over the normaloperating temperatures of an automobile engine compartment. Thiscondition prevails in the case of the automobile on-board computer as asignal source when this signal source is a square wave and the controlis provided by controlling the duty cycle, that is, that percentage ofthe period when the current is allowed to flow. At an elevatedtemperature the duty cycle is increased to compensate for this changedtemperature condition. This is shown in FIG. 10 wherein the outputcurves were produced at two temperatures, 74° F. and 250° F. The resultsclearly show only insignificant changes in the curve positions.

The seat size `y`, as shown in FIG. 6, is relatively large in comparisonto passage 24 diameter. This size difference is to accomodate operationwith a vacuum operator, such as valve 12. Where a high pressure (aboveatmospheric pressure) source is affixed to pole piece 16 at passage end26, a restriction 303 in FIG. 4 is formed in passage 24 and a connectingmeans 302 communicates between passage 24 and a slave motor or pressureoperable device 304. The non-magnetic seat 20 for high pressureoperation is constructed with a diameter generally based upon empiricaltests to determine an operating mode consistent with slave motor 304 andenvironmental operating conditions. However, this seat size for suchhigh pressure operation would be much more narrow relative to passage 24than in the vacuum operation.

While only specific embodiments of the invention have been described andshown, it is apparent that various alterations and modifications can bemade therein. It is, therefore, the intention in the appended claims tocover all such modifications and alterations as may fall within thescope and spirit of the invention.

What is claimed is:
 1. An electromagnetic valve assembly comprising anouter member of a magnetic material, having a top and a bottom;a topmember of a magnetic material, affixed near the top of the outer member;a center member of magnetic material extending through said top memberand positioned generally within the outer member, which center memberhas a bore with an inlet port for receiving fluid, and an exit port; anon-magnetic seat positioned about the exit port and extending beyondthe center member, a base member, attached to the bottom of the outermember to define a chamber adjacent the non-magnetic seat; a magneticclosure member, positioned within the chamber, which closure member is aflat disc armature and, with the outer member, the top member and thecenter member, completes a flux path including an air gap definedbetween the magnetic closure member and said exit port end of the centermember; a reference member of cylindrical shape positioned about thecenter member; and means for establishing the flow of electromagneticflux through said flux path, which means includes an electrical winding,and a bobbin substantially encircling said reference member andsubstantially enclosing the electrical winding, the relative positionsof the center member and the closure member being adjustable to placethe exit port of the center member nearer to or farther from the closuremember and thus regulate the air gap distance, so that for a given levelof flux in the flux path, the closure member will be urged against thenon-magnetic seat as a function of the air gap distance and pressuredifferential between said chamber and said bore.
 2. An electromagneticvalve assembly as claimed in claim 1, and further comprising a springpositioned between said base member and the magnetic closure member, tourge the magnetic closure member toward the nonmagnetic seat.
 3. Anelectromagnetic valve assembly as claimed in claim 1, wherein theclosure member is of a rigid material harder than said non-magneticseat.
 4. An electromagnetic valve assembly as claimed in claim 1,wherein said center member is slidable in the reference member andnon-magnetic seat to regulate the extent of said air gap, and thuscorrespondingly regulate the level of pressure differential between saidchamber and the bore of the center member at which a given level ofelectromagnetic flux in said flux path will actuate said closure memberto sealingly engage said non-magnetic seat.
 5. An electromagnetic valveassembly as claimed in claim 1, wherein the distance between saidnon-magnetic seat and closure member is about one and one-halfthousandth (0.0015) inch at a reference position.
 6. An electromagneticvalve assembly as claimed in claim 1, wherein the non-magnetic seat isbrass.
 7. An electromagnetic valve assembly as claimed in claim 1,operable with a diaphragm operator valve assembly to control the levelof vacuum supplied to a vacuum-operable device.
 8. An electromagneticvalve assembly as claimed in claim 4, wherein said center member isadjusted to a fixed position to maintain a given magnetic flux densityat a reference current flow, to thereby actuate said magnetic closuremember to maintain at least a given level of the differential pressurebetween the chamber and the center member bore.
 9. An electromagneticvalve assembly as claimed in claim 8, wherein the magnetic center memberis fixed in position with respect to the reference member.
 10. Anelectromagnetic valve assembly as claimed in claim 8, wherein themagnetic closure member's mass, the gap distance, non-magnetic seatdiameter, and the magnetic flux density is calibrated to modulate aspecific pressure differential between the center member bore and saidchamber.
 11. An electromagnetic valve assembly as in claim 1, whereinthe surface area of the non-magnetic seat and the magnetic closuremember surface area operate in an inverse manner with respect to eachother to affect the rate of closure member response.
 12. Anelectromagnetic valve assembly as claimed in claim 1, wherein arestriction is positioned in said center member bore near the inlet portsource connection and where a connecting means communicates said bore ata position between said restriction and exit port to a pressure operabledevice.
 13. An electromagnetic valve assembly as claimed in claim 1,wherein the level of electromagnetic flux is a function of the currentinput to the electrical winding.
 14. An electromagnetic valve assemblyas in claim 1, wherein the pressure differential between said bore andchamber at which said closure member will be wedged against said seat isa function of the current input to the electrical winding.
 15. Anelectromagnetic valve assembly as claimed in claim 1, wherein saidreference member and nonmagnetic seat are a single element ofnonmagnetic material.
 16. An electromagnetic valve assembly as claimedin claim 15 wherein said single element is of drawn, thin-wall,nonmagnetic tubing.
 17. An electromagnetic valve assembly as claimed inclaim 1, wherein said bobbin and nonmagnetic seat are a single elementof a nonmagnetic material.
 18. An electromagnetic valve assembly asclaimed in claim 1, wherein said bobbin defines a lower surfacecontacting said chamber, and further comprising a spring positionedbetween said bobbin lower surface and the magnetic closure member, tourge the magnetic closure member away from the nonmagnetic seat.
 19. Anelectromagnetic valve assembly as claimed in claim 18 wherein saidspring maintains said closure member in a reference position relative toa vertical axis of said bore.
 20. An electromagnetic valve assembly asclaimed in claim 1, wherein said base member includes an upstandingcylindrical portion terminating in a generally flat surface area, andfurther comprising a spring positioned around said cylindrical portionand flat surface area between said base member and said magnetic closuremember, to urge the magnetic closure member toward the non-magnetic seatand aid in the positioning of said magnetic closure member.
 21. Anelectromagnetic valve assembly as claimed in claim 1, wherein said flatdisc armature defines at least one aperture.
 22. An electromagneticvalve assembly as claimed in claim 1, wherein the reference member is amagnetic material to augment the flux path.